a) Field of the Invention
The present invention relates to a free-piston type stirling cycle engine, particularly to the structure of a cylinder mounted inside an apparatus body.
b) Prior Art
A stirling cycle engine allows a piston to reciprocate in a cylinder in the axial direction, so that when the piston is shifted toward a displacer, a gas inside a compression chamber formed between the piston and the displacer is compressed, and then it passes through a heat dissipating fin, a regenerator and an endothermic or heat absorbing fin, to reach an expansion chamber formed between the tip end of the displacer and the tip end of a casing, thus pushing the displacer downward. On the other hand, when the piston is shifted to the opposite direction, then the inside of the compression chamber is subjected to a negative pressure, so that the gas returns from the expansion chamber to the compression chamber inside the cylinder, via the heat absorbing fin, the regenerator and the heat dissipating fin, thereby pushing the displacer upwardly. Through such steps, the operation of a reversible cycle consisting of isothermal change and isovolumic change is carried out, whereby the temperature of the heat absorbing fin mounted to the peripheral tip end of the cylinder is lowered, while the temperature of the heat dissipating fin mounted to the outer periphery of a base is raised.
Conventionally, the above-mentioned cylinder has heretofore been produced by machining a pole-shaped metallic material, such as aluminum alloy, steels of various kinds or the like, and there has been a mount portion provided in the cylinder, for the purpose of fixing the cylinder to the casing and retaining a drive mechanism for reciprocating the piston. For improving accuracy, such mount portion would be machined with the same being integral with the cylinder.
However, for forming the cylinder integral with such mount by means of machining process, it is necessary to machine a metallic pole material that is thicker than the outer dimension of the mount, so that a considerable portion of the material becomes metal filing, thus consuming longer time for machining, leading to inferior productivity. Further, as the outer dimension of the mount is comparatively large, a large-sized machining machine is needed, thus causing the increase of costs.
For an alternative method for forming the cylinder with such mount, it is proposed that an approximate configuration may be first obtained by forging or casting a material, and then machining the material. In that case, however, the amount of metal filing is decreased, but the costs are eventually increased due to the forging or casting process prior to the machining process, and thus there is no substantial difference in final costs.
As a further conceivable method for forming the cylinder with such mount, the use of phenolic molding may be considered, which, however, requires a draft angle, and thus at least the machining inside the cylinder is needed, thus leading to a likelihood to degrade the accuracy due to thermal expansion or elastic deformation. As is apparent from the above-mentioned, conventional manufacture of a cylinder integrally formed with a mount has had problems in respect of costs and accuracy.
In addition, as the drive mechanism retained by the mount in a stirling cycle engine reaches a high temperature, there is a risk that the heat of the drive mechanism transfers from the mount to the cylinder, and then transfers to the compression space inside the cylinder, so that the thermal expansion of the cylinder is liable to occur to thereby produce a larger clearance between the cylinder and the piston, and/or the flow of the heat into the compression space is liable to damage the stirling cycle operation itself. Conversely, there has been a risk that the heat inside the compression space transfers to the drive mechanism via the cylinder and the mount, so that the drive mechanism is overheated.
Accordingly, it is a main object of the present invention to provide a stirling cycle engine in which a cylinder with a mount is able to be easily manufactured and installed.
It is another object of the present invention to provide a stirling cycle engine which is subjected to less damage by heat emitted from a drive mechanism.
To attain the above objects, there is provided a stirling cycle engine, comprising: a casing which at least includes a substantially cylinder-shaped cylindrical portion; a metallic cylinder that is coaxially inserted into the cylindrical portion of the casing; a piston inserted into the cylinder; a drive mechanism for reciprocally driving the piston; and a mount which is attached to an outer periphery of said cylinder for fixing the cylinder to said casing and retaining said drive mechanism, wherein said mount is made of a material of low heat conductance, substantially disc-shaped, having an attachment hole in the center thereof. Thus, working process therefor becomes easier, so that the working time is shortened, to thereby improve productivity, and reduce working costs. Further, The heat emitted from the drive mechanism is less likely to be transferred to the cylinder or to the compression chamber inside the cylinder via the mount.
From another aspect of the invention, there is provided a stirling cycle engine as set forth in the preceding paragraph, further comprising: a bar and a male screw which are formed around the outer periphery of said cylinder coaxially therewith; and a recess and a female screw which are formed around an inner periphery of said mount coaxially therewith so that said bar may be inserted into the recess with a slight clearance therebetween and the said male screw may be screwed into the female screw. Thus, the mount can be quite easily and firmly attached to the cylinder.